Step 1Cut the squash in inch-size cubes, discarding the seeds and strings. Steam until tender (about 20 minutes), cut off the peel, then puree the squash in a food processor or food mill. You will need 1 1/2 cups of puree.
Step 2Line a baking sheet with foil and set it on the bottom rack (or middle rack, if you prefer) of the oven; heat the oven to 450 degrees.
Step 3Place the squash, milk, eggs, sugar, molasses, ginger, cinnamon and salt in a mixing bowl. Whisk until the ingredients are thoroughly blended.
Step 4Warm the pastry shell on the baking sheet in the oven for 5 minutes.
Step 5Remove the baking sheet and shell from the oven. Whisk the custard to blend once again, then pour through a fine sieve into the shell.
Step 6Set the baking sheet and shell in the oven and bake 10 minutes. If on the bottom rack, carefully move the sheet and pie up to the center rack. Place a tent of foil over the pie, shiny side up. Reduce the temperature to 350 degrees and continue baking until the custard tests ready to remove using the quarter test (remove the pie when the distinct pool of unset custard in the center has shrunk to the size of a quarter) or the knife test (insert a table knife just off-center, and when it comes out with solid bits of custard attached, it's ready)--about 40 minutes more. Cool; then, if necessary, refrigerate until an hour or so before serving with a dollop of unsweetened whipped cream.